The subject matter disclosed herein relates to turbine components and, more specifically, to processes and systems for treating turbine component surfaces comprising one or more fluid flow passages.
In gas turbine engines, such as aircraft engines for example, air is drawn into the front of the engine, compressed by a shaft-mounted rotary-type compressor, and mixed with fuel. The mixture is burned, and the hot exhaust gases are passed through a turbine mounted on a shaft. The flow of gas turns the turbine, which turns the shaft and drives the compressor and fan. The hot exhaust gases flow from the back of the engine, driving it and the aircraft forward.
During operation of gas turbine engines, the temperatures of combustion gases may exceed 3,000° F., considerably higher than the melting temperatures of the metal parts of the engine which are in contact with these gases. Operation of these engines at gas temperatures that are above the metal part melting temperatures can depend in part on supplying a cooling air to the outer surfaces of the metal parts through various methods. The metal parts of these engines that are particularly subject to high temperatures, and thus require particular attention with respect to cooling, are the metal parts forming combustors and parts located aft of the combustor.
The metal temperatures can be maintained below melting levels by using fluid flow passages (also known as cooling holes) incorporated into some engine components. Sometimes, one or more coatings such as thermal barrier coatings (TBCs) may also be applied to the component by a thermal spray process. However, coating processes such as the thermal spray process and other cleaning processes (e.g., grit blasting, shot peening, water jet washing) may result in overspray that partially or completely blocks the component's cooling holes.
As a result, present coating and cleaning processes can involve a multi-step process of applying a partial layer coating (e.g., TBC coating), allowing the component and the coating to sufficiently cool to a temperature at which the component can easily be handled, removing the component from an application fixture on which the thermal spraying takes place, and removing any masking, which is then followed by separately removing the well-cooled, solidified coating from the fluid flow passages using a water jet or other cleaning methods. To prevent the fluid flow passages from becoming obstructed beyond a level from which they can be satisfactorily cleaned, only a fraction of the desired coating thickness may be applied prior to cleaning. As a result, the entire process may need to be repeated several times until the desired coating thickness is reached. This process can result in low productivity, high cycle time, and increases costs by a factor of five to ten times that of applying the same coating to a similar non-holed part. Even when coatings are not applied, the pressure cleaning methods used to clean the target surfaces of articles can similarly overflow and obstruct or affect the article's fluid flow passages.
Accordingly, alternative turbine component surface treatment processes and systems would be welcomed in the art.